1. Field of the Invention
This invention pertains to a electrosurgical instrument and a method for its manufacture. More specifically, the present invention pertains to a disposable and/or reusable electrosurgical blade which inhibits the build up of charred tissue, and is therefore able to slide through tissue when making an incision, and perform cauterization functions with a minimal amount of thermal damage to surrounding tissues.
2. State of the art
State of the art electrosurgical blades are utilized in surgery to provide both a blade for incising through normal tissue and for excising abnormal tissue. The electrosurgical blade directs a source of radio-frequency (RF) energy to the tissue to thereby perform cauterizing (hemostasis) functions such as coagulation, fulguration and desiccation. Ideally, the electrosurgical blade is utilized to effectively cut tissue while at the same time minimizing the amount of bleeding.
The amount and type of radio frequency energy delivered to tissue through the electrosurgical blade is varied depending upon the activity being performed. Cutting is achieved primarily with a continuous sinusoidal waveform. In contrast, coagulation is performed with a series of sinusoidal wave packets. The clinician is ideally able to elect one of these waveforms, or a blend of them for a particular surgical procedure.
An electrosurgical blade can operate in one of two modes which are defined by the method by which electrical current enters and leaves the tissue. In a monopolar mode, the current flows from a small active electrode (the electrosurgical blade), spreads through the body, and returns to a large dispersive electrode on the skin. In contrast, the bipolar mode delivers electrical current to tissue which is disposed between two electrodes which are generally spaced apart to form a gap. The monopolar mode is used for both cutting and coagulation, and the bipolar mode is used primarily for coagulation.
While using electrosurgical instruments, tissue is inevitably charred during surgery and will try to cling to the heat source. When the heat source is the electrosurgical blade, the charred tissue interferes with the performance of the electrosurgical blade. Performance degradation of the blade poses serious problems when trying to minimize heat damage to a patient's tissues.
One of the specific problems which electrosurgical blades presently suffer from and which is caused by the build up of charred tissue is that cutting efficiency is reduced. The typical response to such residual tissue build up is to increase current to the electrosurgical blade to compensate. However, increased current poses a more serious shock hazard to the patient as well as the physician. It also raises the possibility of more easily and rapidly charring tissue. This is because some exposed surfaces of the electrosurgical blade will have charred tissue adhering thereto, but other surfaces will be free of charred tissue and will therefore deliver more current to tissue at a faster rate.
Another problem resulting from the build up of charred tissue is that the charred tissue can fracture off of the blade. The fractured tissue becomes an undesired foreign body within the surgical field. The fractured tissue can then interfere with the surgical procedure being performed, increase the inflammatory response, and delay the healing process.
The build up of charred tissue also causes the electrosurgical blade to pass through tissue with increasing resistance or drag. This drag tends to distort the tissue and consequently alter anatomical relationships. This can create problems when suturing after the surgical procedure, and possibly delay healing, and result in more visible scarring.
The burning of charred tissue also generates hazardous smoke plumes. Inhalation of the smoke endangers those performing a surgical procedure.
The consequence of the build up of charred tissue is that the procedure is interrupted, while the electrosurgical blade must either be replaced, or passed to an operating room (OR) technician who scrapes off the build up before the clinician continues with the surgical procedure.
The problems described above have been dealt with by various electrosurgical blades. For example, prior U.S. patents have been issued for various electrosurgical blades which apply a non-stick coating to a cutting edge of the blade. These blades typically suffered from small openings in the non-stick coating which were intentionally allowed to form in order to ensure electrical conductivity along the cutting edge. Exposing the metallic surface of the blade resulted in charred tissue sticking to these areas. The result was that the blade quickly becomes non-conductive and consequently unusable.
In an attempt to improve the blade, Blanch was granted U.S. Pat. No. 4,785,807 (the '807 patent) for teaching an electrosurgical blade which has a cutting edge of the blade which is abraded or etched, and a coat of a non-stick fluorinated hydrocarbon material which is applied over the etched cutting edge. This electrosurgical blade is shown in FIG. 1. The blade 4 is shown with a proximal end 8 and a distal end 16. A coating 20 of non-stick material covers the surface area of the cutting blade and is intended to eliminate or reduce the clinging of charred tissue to the blade. By eliminating the small openings in the non-stick coating of previous blades, the blade 4 better inhibited the build up of charred tissue. However, one drawback in the principle of the '807 patent is that the non-stick coating 20 is not particularly durable, and will wear off after repeated usage. This is true partly because the non-stick and non-conductive coating 20 has the properties of an insulator and had to be kept thin in order to enable the radio-frequency energy to pass through the non-stick coating 20 to the tissue to cut and/or cauterize.
Another drawback of the blade described in the '807 patent is that the non-stick coating is not flexible. This inability to bend the electrosurgical blade seriously limits the options of the surgeon in the surgical procedures in which the blade can be used. Furthermore, bending the electrosurgical blade causes the non-stick coating to fracture. The electrosurgical blade then begins to rapidly build up charred tissue because of exposed etched metal of the blade, and any advantages of the non-stick coating are lost.
The non-stick coating of the '807 patent is also specifically described as Teflon.TM.. The nature of Teflon.TM. is such that it requires a high current to be used in cutting and cauterization. This is because electrical current must pass through the Teflon.TM. to the tissue. However, this constant passage of current eventually breaks down the Teflon.TM., leaving small holes or other imperfections in the Teflon.TM. coating. Charred tissue then begins to adhere to the exposed metal beneath the Teflon.TM. coating. Furthermore, electrical current will no longer be uniform across the blade because the current will tend to concentrate at locations where the metal is exposed.
The state of the art includes at least one electrosurgical blade which is made of a ceramic. The ceramic is used as an insulator on which a tungsten wire is placed on a cutting edge of the ceramic blade. Radio frequency energy is then applied to the tungsten wire which facilitates cutting of tissue. However, this ceramic blade cannot be bent and does not provide a flat surface for cauterization, so its application to a variety of different surgical procedures is very limited.
It is also a typical perception that ceramics do not make a good electrosurgical blade because ceramics exhibit properties of brittleness, inflexibility, and act as insulators rather than conductors of electrical or radio frequency energy.
Another state of the art electrosurgical blade is fashioned from a polymer. The polymer is doped with conductive particles to make it conductive of the radio frequency energy which is used to heat tissue. A trend toward using plastics was most likely fostered by the view that plastics are inexpensive, the property of lubricity of plastics is desirable in electrosurgical blades, and the process of applying plastic as a coating is relatively simple.
Another problem in the state of the art electrosurgical blades which utilize Teflon.TM. is that when heated, Teflon disadvantageously breaks down and evolves fluorine as a gas. This gas is hazardous to the patient and the surgical team.
It would be an advantage over the state of the art to provide, among other things, an electrosurgical blade which better inhibits the build up of charred tissue, provides a more durable non-stick coating which can withstand repeated use and cleaning, and which provides an amorphous or amorphous-like conductive coating which enables the electrosurgical blade to bend so as to perform a larger variety of surgical procedures at low power levels, without the risk of damaging or breaking down the coating and causing tissue build up. It would be a further advantage to provide a protective coating which does not evolve gases when heated.